1. Field of the Invention
The invention relates to a vehicle that includes an alternating-current motor that is controlled through pulse width modulation (hereinafter, also referred to as “PWM”) control.
2. Description of Related Art
An output torque of a motor that is mounted on an electromotive vehicle, such as an electric vehicle, a hybrid vehicle and a fuel-cell vehicle, is generally controlled through PWM control. In this PWM control, a pulse width modulation voltage is applied to the motor from an inverter by turning on or off switching elements of the inverter on the basis of a voltage comparison between a carrier wave signal (carrier signal) and a voltage command.
Japanese Patent Application Publication No. 2-179297 (JP 2-179297 A) describes the following technique. That is, when there occurs an abnormality in a motor, a control period and control frequency of the inverter through PWM control are changed. By so doing, an electromagnetic sound that is generated from the motor is changed by changing a ripple frequency of phase current flowing through the motor. Japanese Patent Application Publication No. 2-179297 discloses the technique for informing a user of an abnormality of the motor through a change of the electromagnetic sound.
In a vehicle that includes an alternating-current motor that is controlled through PWM control, it is possible to intentionally generate a sound from the motor by periodically changing phase current flowing through the motor. However, if the rotation speed of the motor steeply varies due to a slip, or the like, of a drive wheel, phase current flowing through the motor may be in an overcurrent state in which phase current exceeds a permissible value. However, JP 2-179297 A does not describe such a problem and its solution.